Method of manufacturing a semiconductor device with an L-shape/reversed L-shaped gate side-wall insulating film

ABSTRACT

Provided is a semiconductor device, comprising a gate electrode formed on a semiconductor substrate, source/drain diffusion layers formed on both sides of the gate electrode, a gate electrode side-wall on the side of the source/drain diffusion layer and a gate side-wall insulating film covering a part of the upper surface of the semiconductor substrate in the vicinity of the gate electrode and having an L-shaped/reversed L-shaped cross-sectional shape, and a semiconductor layer extending over the gate side-wall insulating film covering a part of the upper surface of the semiconductor substrate in the vicinity of the gate electrode.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is based upon and claims the benefit of priorityfrom the prior Japanese Patent Application No. 2000-397293, filed Dec.27, 2000, the entire contents of which are incorporated herein byreference.

BACKGROUND

[0002] 1. Field of the Invention

[0003] In recent years, shrinking of a CMOS-type semiconductor device isbeing promoted in compliance with the request for the high-speedoperation and the high-performance of the device. In accordance withprogress in the shrinking, the scaling of the distance between the gateand the source/drain contact is required.

[0004] 2. Description of the Related Art

[0005] The problems relating to the shrinking of the high-performanceMOS transistor equipped with a silicide electrode will now be described.

[0006]FIG. 1A is a cross-sectional view showing the construction of ahigh-performance MOS transistor equipped with a silicide electrode. TheMOS transistor shown in FIG. 1A comprises a Si substrate 101, a deviceisolation insulating film 102 of a shallow trench isolation (STI), agate electrode formed of a polycrystalline silicon (polysilicon) film106 formed on the Si substrate 101 with a gate insulating film 105interposed therebetween, a shallow source/drain diffusion layer 107formed by ion implantation with the gate electrode used as a mask, agate side-wall insulating film 109 formed on the side-wall of the gateelectrode, a deep source/drain diffusion layer 111 of a high impurityconcentration formed by ion implantation with the gate electrodeequipped with the gate side-wall insulating film 109 used as a mask, anda metal silicide layer 112 such as a cobalt silicide layer formed on theexposed surface of the deep source/drain diffusion layer 111 of a highimpurity concentration and on the gate electrode formed of thepolysilicon layer 106. A mark S₁ shown in FIG. 1A denotes the lengthshowing the expansion in the direction of the gate length of the metalsilicide film covering the deep source/drain diffusion layer 111 of ahigh impurity concentration.

[0007] In shrinking the semiconductor device, it is absolutely necessaryto decrease the width of the gate side-wall insulating film 109 inaccordance with the scaling. Also, it is necessary to increase to someextent the depth of the deep source/drain diffusion layer 111 of a highimpurity concentration in view of the generation of the leakage currentin the junction surface between the deep source/drain diffusion layer111 of a high impurity concentration having the silicided surface andthe Si substrate 101. If the width of the gate side-wall insulating film109 is decreased in this case, it is impossible to suppress theshort-channel effect produced by the deep source/drain diffusion layer111 of a high impurity concentration, with the result that it isdifficult to shrink the width of the gate side-wall by the scaling inthe high-performance MOS transistor equipped with a silicide electrode.

[0008] On the other hand, if the distance S₁ between the edge of thegate side-wall insulating film 109 and the peripheral portion on theside of the source/drain of the device isolation insulating film 102 ofSTI is decreased by the scaling, the area of the metal silicide layerformed on the deep source/drain diffusion layer of a high impurityconcentration is decreased so as to increase the parasitic resistance.Particularly, in the case of using the MOS transistor structure of acorner contact type, in which a contact hole is formed in the cornerportion of the source/drain forming region, the increase in theparasitic resistance constitutes a serious problem.

[0009] In conjunction with the problem described above, the method offorming a contact hole for connecting the source/drain regions of ahigh-performance MOS transistor equipped with a silicide electrode tothe wiring on the semiconductor substrate and the problems accompanyingthe forming method will now be described in detail with reference toFIG. 1B.

[0010]FIG. 1B is a cross-sectional view showing the step of forming acontact hole in a high-performance MOS transistor equipped with asilicide electrode. As shown in the drawing, an interlayer insulatingfilm 118 is formed to cover a high-performance MOS transistor equippedwith silicide electrodes isolated from each other by the deviceisolation insulating film 102 of STI, followed by forming a contact hole119 in the interlayer insulating film 118 by aligning a mask with themetal silicide layer 112 on the deep source/drain diffusion layer of ahigh impurity concentration by using a resist (not shown) andlithography.

[0011] In this case, if the length S₁ shown in FIG. 1A is shrunk by thescaling, a mask misalignment is generated as shown in FIG. 1B, with theresult that the contact hole 119 partly reaches the gate side-wallinsulating film 109 so as to markedly decrease the distance S₂corresponding to the contact area with the metal silicide layer 112.

[0012] The connection between the metal wiring (not shown) on thesemiconductor substrate and the metal silicide layer 112 is achieved byburying a contact plug made of a metallic material in the contact hole119. Therefore, if the distance S₂ is decreased, the parasiticresistance between the source and drain of the MOS transistor isincreased so as to lower the operating speed.

[0013] Also, with progress in the development of the semiconductordevice, it is necessary to make shallower not only the shallowsource/drain diffusion layer 107 of the MOS transistor but also the deepsource/drain diffusion layer 111 of a high impurity concentration.However, as described previously, if the source/drain diffusion layer111 of a high impurity concentration is made shallower, the generationof the contact leakage in forming the silicide layer 112 and theincrease in the power consumption of the CMOS circuit accompanying thegeneration of the contact leakage are brought about as new problems. Asa measure for overcoming these problems, proposed is a MOS transistor ofan elevated source/drain structure.

[0014] The MOS transistor of this type is constructed such that a singlecrystal Si or SiGe layer is formed selectively by means of an epitaxialgrowth on a source/drain diffusion region of a high impurityconcentration, and the impurity concentration in the surface region ofthe Si substrate including the epitaxial growth layer is increased so asto make the high impurity concentration diffusion layer in the Sisubstrate substantially shallower.

[0015] In the case of using the elevated source/drain structure, thesurface region of the single crystal Si or SiGe layer grown by theselective epitaxial method on the source/drain diffusion region isconverted into a silicide region so as to make it possible to avoid thegeneration of the contact leakage current.

[0016] In applying the elevated source/drain structure, it is absolutelynecessary in allowing the CMOS circuit to operate normally to ensure thedevice isolation characteristics of STI so as to prevent completely asingle crystal Si or SiGe layer from growing on the upper surfaces ofthe device isolation insulating film 102 of STI and the gate side-wallinsulating film 109 and to allow the epitaxial growth layer to be formedselectively only on the upper surface of the source/drain diffusionregion.

[0017] However, in the STI having a small separation width, the buriedstate is rendered poor when the device isolation insulating film 102 isburied in the trench so as to generate a seam of the device isolationinsulating film in the central portion of the trench width in thelongitudinal direction of the trench, as described in, for example, Jpn.Pat. Appln. KOKAI Publication No. 58-143548 and Jpn. Pat. Appln. KOKAIPublication No. 1-151245. In this case, if the epitaxial growth layer isselectively formed on the source/drain diffusion region, Si or SiGeparticles are generated in the central portion in the width direction ofthe STI with the portion of the seam providing the growth nucleus.

[0018] The failure generation of the device isolation characteristics inthe elevated source/drain structure will now be described more in detailwith reference to FIGS. 2A and 2B. FIG. 2A is a cross-sectional viewshowing the normal STI structure in the elevated source/drain structure.The device isolation insulating film 102 of STI shown in FIG. 2A isburied satisfactorily in the trench because the trench has a largewidth, with the result that a seam generation is not recognized in thecentral portion of the STI. It follows that, if an epitaxial growthlayer 110 is selectively formed on the Si substrate 101, the epitaxialgrowth layer 110 is formed in the peripheral portion of the deviceisolation insulating film 102 in which the STI is contiguous to the Sisubstrate 101. However, since a Si layer is not grown in the centralportion of the device isolation insulating film 102, good deviceisolation characteristics can be assured.

[0019] However, if the trench width is small as shown in FIG. 2B, adevice isolation insulating film 116 fails to be buried satisfactorilyin the trench, with the result that a seam 117 of the device isolationinsulating film 116 is generated in the central portion of the trenchwidth in the longitudinal direction of the trench. In the surface of thedevice isolation insulating film 116 in which is generated the seam 117,the surface selectivity with the surface of the Si substrate is loweredin the process of the epitaxial growth, with the result that Si or SiGeparticles 110 a are generated with the seam 117 providing the nucleus ofthe growth. As a result, the leakage current on the surface of thedevice isolation insulating film 116 is increased so as to lower thedevice isolation characteristics of the STI, leading to the occurrenceof a short-circuit. Incidentally, the deep source/drain diffusion layer111 of a high impurity concentration is omitted from each of FIGS. 2Aand 2B so as to simplify the drawing.

[0020] As described above, the performance of the MOS transistor isimproved in the prior art by utilizing the elevated source/drainstructure. However, since it is difficult to shrink the gate side-wallinsulating film by means of scaling, the area of the contact on thesource/drain region is decreased so as to give rise to the problem thatthe connection to the wiring by the contact hole is rendered difficult.

[0021] It should also be noted that, in accordance with the shrinking ofthe STI, a seam is generated in the device isolation insulating filmwhen the device isolation insulating film is buried in the trench, withthe result that, if a Si or SiGe layer is formed by a selectiveepitaxial growth method on the source/drain diffusion layer, Si or SiGeparticles are generated on the device isolation insulating film with theseam providing the nucleus of the growth so as to give rise to theproblem that the device isolation characteristics of the STI aredegraded.

[0022] Each of the embodiments of the present invention described belowprovides a semiconductor device that permits assuring the contact areaon the source/drain region regardless of the shrinking of the transistorstructure by the scaling and a method of manufacturing the particularsemiconductor device. Each of the embodiments of the present inventionalso provides a semiconductor device that permits assuring a highsurface selectivity between the surface of the device isolationinsulating film buried in the STI and the surface of the substrate onthe source/drain diffusion layer so as to make it possible to realize anelevated source/drain structure while maintaining good device isolationcharacteristics of the STI and a method of manufacturing the particularsemiconductor device.

SUMMARY

[0023] A semiconductor device according to an embodiment of the presentinvention comprises a gate electrode formed on a semiconductorsubstrate, source/drain diffusion layers formed on both sides of thegate electrode, a gate side-wall insulating film having anL-shaped/reversed L-shaped cross-sectional shape covering the gateelectrode side-wall on the side of the source/drain diffusion layer anda part of the upper surface of the semiconductor substrate in thevicinity of the gate electrode, and a semiconductor layer formed on thesource/drain diffusion layer and extending to cover the gate side-wallinsulating film covering a part of the upper surface of thesemiconductor substrate in the vicinity of the gate electrode.

[0024] A semiconductor device according to another embodiment of thepresent invention comprises a buried device isolation region including atrench formed in an upper surface region of a semiconductor substrate, afirst buried insulating film formed to extend along the inner wall ofthe trench in a manner to be buried in a lower portion of the trench toreach a predetermined depth from the open surface of the trench, and asecond buried insulating film formed to cover the first buriedinsulating film in an upper portion of the trench.

[0025] Further, a method of manufacturing a semiconductor deviceaccording to still another embodiment of the present invention comprisesforming a gate electrode on a semiconductor substrate with a gateinsulating film interposed therebetween, forming a shallow source/draindiffusion layer in those regions of the semiconductor substrate whichare positioned on both sides of the gate electrode by means of ionimplantation performed with the gate electrode used as a mask, forming afirst side-wall insulating film on the semiconductor substrate afterformation of the shallow source/drain diffusion layers, forming a secondside-wall insulating film on the first side-wall insulating film,etching back a laminate structure including the first side-wallinsulating film and the second side-wall insulating film, removing thesecond side-wall insulating film remaining on the side-wall portion ofthe gate electrode so as to form an L-shaped/reversed L-shaped side-wallstructure consisting of the first side-wall insulating film covering thegate electrode side-wall portion and a part of the upper surface of thesemiconductor substrate in the vicinity of the gate electrode, forming asemiconductor layer thicker than the first side-wall insulating film onthe semiconductor substrate by means of a selective epitaxial growthmethod so as to form an extending portion of the semiconductor layer onthe first side-wall insulating film covering a part of the upper surfaceof the semiconductor substrate, and forming deep source/drain diffusionlayers in those portions of the semiconductor substrate which arepositioned on both sides of the gate electrode by means of ionimplantation performed with the gate electrode equipped with theside-wall structure used as a mask.

BRIEF DESCRIPTION OF THE DRAWINGS

[0026]FIGS. 1A and 1B are cross-sectional views collectively showing theconstruction of and the problem inherent in an elevated source/drain MOStransistor;

[0027]FIGS. 2A and 2B are cross-sectional views collectively showing theconstruction of and the problem inherent in the STI structure;

[0028]FIGS. 3A to 3E are cross-sectional views collectively showing amethod of manufacturing a semiconductor device according to a firstembodiment of the present invention;

[0029]FIG. 4 is a cross-sectional view showing the construction of theSTI structure according to a second embodiment of the present invention;and

[0030]FIGS. 5A to 5F are cross-sectional views collectively showing amethod of manufacturing an STI according to the second embodiment of thepresent invention.

DETAILED DESCRIPTION

[0031] Some embodiments of the present invention will now be describedin detail with reference to the accompanying drawings.

[0032] <First Embodiment>

[0033]FIGS. 3A to 3E are cross-sectional views collectively showing themanufacturing process and the construction of a high-performance MOStransistor of an elevated source/drain structure constituting asemiconductor device according to a first embodiment of the presentinvention.

[0034] As shown in FIG. 3A, an STI is formed by burying a deviceisolation insulating film 2 in a shallow trench formed in a p-type orn-type Si substrate 1 in a depth of 200 to 350 nm. Then, an oxide filmis formed in a thickness not larger than 20 nm on the surface of the Sisubstrate 1 in the active element forming region between the STI's shownin FIG. 3A, followed by forming a well region 3 and a channel region 4by means of ion implantation of an impurity through the oxide film.Further, the implanted impurity is subjected to an activation heattreatment by utilizing a rapid thermal annealing (RTA).

[0035] Concerning the typical conditions of the ion implantation,phosphorus (P) is implanted into the n-well region 3 under anaccelerating energy of 500 keV and at a dose amount of 3.0E13 cm⁻².Boron (B) is implanted into the channel region 4 under an acceleratingenergy of 50 keV and at a dose amount of 1.5E13 cm⁻². Boron (B) isimplanted into a p-well under an accelerating energy of 260 keV and at adose amount of 2.0E13 cm⁻². Further, phosphorus (P) is implanted intothe channel region within the p-well under an accelerating energy of 130keV and at a dose amount of 1.5E13 cm⁻².

[0036] Then, after removal of the oxide film on the surface of thesubstrate, a gate oxide film 5 is formed in a thickness of 1.5 to 6 nmby means of a thermal oxidation or a low-pressure chemical vapordeposition (LPCVD), followed by depositing a polysilicon layer in athickness of 100 to 200 nm on the gate oxide film 5. Then, patterning ofa gate electrode having a gate length of 20 to 150 nm is performed byemploying a light, X-ray or electron-beam lithography, followed by anetching using a reactive ion etching (RIE) so as to form a gateelectrode consisting of the polysilicon layer 6.

[0037] It is possible for the gate insulating film to be formed of SiON,SiN or a material having a high dielectric constant such as Ta₂O₅ inaddition to the gate oxide film 5 made of SiO₂. It is also possible toemploy in place of the polysilicon layer 6 a metal gate structure using,for example, tungsten (W) having a high conductivity as a material ofthe gate electrode with, for example, TiN or WN used as a barrier metal.

[0038] In the next step, a thermal oxide film having a thickness of 2 to6 nm is formed as a post oxidation, followed by implanting impurity ionswith the gate electrode used as a mask so as to form shallowsource/drain diffusion layers 7 on both sides of the gate electrode.Further, an activation heat treatment of the implanted ions is performedby means of an RTA. Concerning the typical conditions of the ionimplantation, arsenic (As) is implanted into an n-type shallow diffusionlayer under an accelerating energy of 0.5 to 5.0 keV and at a doseamount of 5.0E14 to 2.0E15 cm⁻². Also, BF₂ or Boron is implanted into ap-type shallow diffusion layer under an acceleration energy of 0.2 to3.0 keV and at a dose amount of 5.0E14 to 2.0E15 cm⁻².

[0039] Then, after removal of the thermal oxide film by the postoxidation, a silicon nitride film 8 and a silicon oxide film 9 aredeposited by the LPCVD method on the entire surface of the Si substrate1 having the gate electrode formed thereon with the gate oxide film 5interposed therebetween. Further, a laminate structure including thesilicon nitride film 8 and the silicon oxide film 9 is etched back byRIE until the laminate structure positioned on the gate electrode and onthe Si substrate 1 is removed, thereby forming a gate side-wallinsulating film including the silicon nitride film 8 and the siliconoxide film 9, as shown in FIG. 3B. Incidentally, it is conceivable for asilicon oxide film to be formed below the silicon nitride film 8 as wellas on the silicon nitride film 8.

[0040] In this case, the upper surface of the Si substrate 1 in theshallow source/drain diffusion layers 7 is exposed to the RIE treatment,with the result that a damaged layer or a carbon layer is mixed in theSi substrate. Therefore, in order to obtain the surface of the Sisubstrate 1 free from damage, the surface of the Si substrate 1 isoxidized by means of an O₂ RIE, followed by removing the oxidizedsurface layer with diluted hydrofluoric acid.

[0041] In the next step, the silicon oxide film 9 covering the siliconnitride film 8 is removed by using diluted hydrofluoric acid so as toform a gate side-wall insulating film consisting of the silicon nitridefilm 8 having an L-shaped and a reversed L-shaped cross-sectional shapeas shown in FIG. 3C. Then, a heat treatment is performed at a hightemperature under a hydrogen gas atmosphere so as to remove the nativeoxide film, thereby selectively forming a Si or SiGe layer 10 by theepitaxial growth on the exposed surface of the Si substrate 1 on theshallow source/drain diffusion layers 7.

[0042] The process of the epitaxial growth is performed by heating theSi substrate, etc., under a hydrogen gas atmosphere at a hightemperature not lower than 800° C., and supplying a source gas such asSiH₄, SiH₂Cl₂ or SiHCl₃ onto the Si substrate together with hydrogengas. Alternatively, a source gas such as GeH₂, GeH₂Cl₂ or GeHCl₃ issupplied onto the Si substrate together with hydrogen gas under ahydrogen gas atmosphere of about 650° C. so as to permit a Si or SiGelayer 10 to grow selectively on the surface of the Si substrate 1exposed on the shallow source/drain diffusion layers 7 or only on thesurface of the polysilicon layer 6 exposed on the upper surface of thegate electrode.

[0043] In this case, it is possible to cap the gate electrode formed ofthe polysilicon film 6 with an insulating film so as to prevent the Sior SiGe layer 10 from growing on the gate electrode and to allow the Sior SiGe layer 10 to grow selectively only on the upper surfaces of theshallow source/drain layers 7. The apparatus used for the selectiveepitaxial growth of the Si or SiGe layer 10 includes a vertical type, abarrel type and a cluster type. The heating method includes resistanceheating, high-frequency heating, and lamp heating. Further, the waferprocessing scheme can be classified into a one-wafer scheme and a waferbatch scheme. Any of these techniques can be employed for the epitaxialgrowth in the present invention.

[0044] In the first embodiment of the present invention, the thicknessof the Si or SiGe layer 10 grown on the upper surface of the shallowsource/drain diffusion layers 7 is set larger than the thickness of thegate side-wall insulating film formed of the silicon nitride film 8 asshown in FIG. 3C so as to allow the Si or SiGe layer 10 to cover theupper surface of the L-shaped or reversed L-shaped silicon nitride film8 covering a part of the upper surface of the Si substrate in thevicinity of the gate electrode formed of the polysilicon layer 6. Inthis case, the Si or SiGe layer 10 also grows to cover the peripheralregion of the device isolation insulating film 2 buried in the STI, withthe result that it is possible to increase the area of the formingregion of the Si or SiGe layer 10.

[0045] In the next step, if there is a capping layer above the gateelectrode, the etching of this layer is performed, and a source/draindiffusion layer 11 having a high impurity concentration is formed bymeans of ion implantation through the Si or SiGe layer 10 with the gateelectrode provided with the gate side-wall insulating film formed of thesilicon nitride film 8 used as a mask so as to form an elevatedsource/drain structure, as shown in FIG. 3D. Incidentally, the order ofthe manufacturing steps described above is no more than an example. Forexample, it is possible to form first the source/drain diffusion layerof a high impurity concentration, followed by growing the Si or SiGelayer 10. The present invention is not necessarily limited to the orderof the manufacturing steps described above.

[0046] In order to suppress the short channel effect of the MOStransistor, it is desirable for the relationship described below to beestablished between the depth of the source/drain diffusion layer of ahigh impurity concentration and the size in the vicinity of the gateelectrode masked by the gate side-wall insulating film.

[0047] Specifically, the gate side-wall insulating films formed of theL-shaped and reversed L-shaped silicon nitride film 8 are formed tocover partly the upper surface of the semiconductor substrate (uppersurfaces of the source/drain regions) in the vicinity of the gateelectrode. In the present invention, the length SW, in the direction ofthe gate length, of the upper surface of the semiconductor substratecovered with the gate side-wall insulating film (length of the lowerside of the L-shape of the gate side-wall insulating film) is set tofall within a range of Xj×0.4≦SW≦Xj×0.8, where Xj represents thejunction depth of the source/drain diffusion layer 11 of a high impurityconcentration.

[0048] In the next step, a metal silicide layer 12 is formed in aself-aligned manner. For example, a metal film consisting of, forexample, Ti, Co or Ni is formed on the entire surface, followed byapplying heat treatment so as to convert the upper region of the siliconlayer into the metal silicide layer 12. Then, the unreacted metal layeris removed so as to obtain a MOS transistor of an elevated source/drainstructure having a small series resistance in the electrode portion.

[0049] It is also possible to form a poly-metal structure on the gateelectrode in place of the metal silicide layer 12 in order to furtherdecrease the gate resistance. For forming the poly-metal structure, abarrier metal layer of a TiN layer or a WN layer is formed directly onthe polysilicon layer 6, followed by depositing a W layer having a highconductivity on the barrier metal layer. Also, it is conceivable for thegate electrode to be formed of polycrystalline silicon germanium(poly-SiGe).

[0050] In the next step, TEOS, BPSG, SiN, or the like is deposited toform an interlayer insulating film (not shown), followed by planarizingthe surface of the interlayer insulating film by means of CMP. Then, acontact hole is formed in conformity with the silicide layer 12 of thesource/drain region by using a resist mask and the RIE method, followedby forming a barrier metal layer of, for example, Ti or TiN on the innerwall of the contact hole. Further, W is blanketed or selectively grownin a manner to fill the contact hole, followed by applying a CMPtreatment to the formed W layer so as to form a contact plug serving toconnect the wiring to the source/drain regions. Finally, afterdeposition of a metal for the wiring, the wiring is patterned so as tofinish the manufacture of a high-performance semiconductor deviceaccording to the first embodiment of the present invention.

[0051] In the semiconductor device according to the first embodiment ofthe present invention, the epitaxially grown layer, which is convertedinto a metal silicide layer to form the source/drain electrode, has alarge area even if the MOS transistor is miniaturized so as to make itpossible to increase the mask alignment margin of the contact holeconnected to the wiring and, thus, to provide easily a semiconductordevice having a low parasitic resistance.

[0052] Incidentally, in the description given above, the Si or SiGelayer 10 is converted into a single crystal on the substrate 1 exposedto the source/drain region. However, the Si or SiGe layer 10 is notnecessarily converted into a single crystal on the silicon nitride film8, the device isolation insulating film 2 and the polysilicon layer 6,but possibly remains to be polycrystalline. In the first embodiment ofthe present invention, no particular problem is generated even if the Sior SiGe layer 10 is partly converted into a polycrystalline state.

[0053] <Second Embodiment>

[0054] The STI structure of a semiconductor device according to a secondembodiment of the present invention and the manufacturing method thereofwill now be described with reference to FIGS. 4 and 5A to 5F.

[0055]FIG. 4 is a cross-sectional view showing the construction of thedevice isolation insulating film buried in the STI and the peripheralportion thereof. The construction shown in FIG. 4 comprises a Sisubstrate 1, a gate electrode including a polysilicon layer 6, etc., agate side-wall insulating film formed of, for example, a silicon oxidefilm 9, a Si or SiGe layer 10 formed on the source/drain region (notshown) and the gate electrode, a first device isolation insulating film16 buried in the bottom portion of a trench forming the STI, a seam 17generated inside the first device isolation insulating film 16 withinthe trench, and a second device isolation insulating film 18 buried inan upper portion of the opening of the trench and not containing a seam.Incidentally, it is possible for the first device isolation insulatingfilm 16 not to include a seam depending on the separation width of theSTI and the etching amount of the first device isolation film 16.

[0056] The second embodiment is directed to the construction of thefirst and second device isolation insulating films 16, 18 buried in theSTI and the surface selectivity of the STI surface in the step of theepitaxial growth of the Si or SiGe layer 10 on the surface of the Sisubstrate. Such being the situation, the construction of the transistorseparated by the STI is shown in a simplified manner for avoiding thecomplexity of the drawing.

[0057] As described previously in conjunction with FIG. 2B, a seam ofthe device isolation insulating film is generated in the central portionof the separation width in the longitudinal direction of the STI if theseparation width of the STI is decreased in accordance with theminiaturization, with the result that Si or SiGe particles are generatedwith the seam providing the nucleus of the growth. As a result, thedevice isolation characteristics are rendered poor. In the STI accordingto the second embodiment of the present invention, however, the openportion of the trench is covered with the flat second device isolationinsulating film 18 that does not include a seam, as shown in FIG. 4. Asa result, in the epitaxial growth of the Si or SiGe layer 10, theepitaxial layer is grown from the surface of the Si substrate 1 in amanner to overhang the peripheral portion of the opening of the trench.However, a crystal grain is not generated in the central portion of theseparation width. It follows that it is possible to assure goodseparation characteristics of the STI.

[0058] The manufacturing method of the STI according to the secondembodiment of the present invention will now be described with referenceto FIGS. 5A to 5F.

[0059] In the first step, a silicon oxide film (not shown) having athickness of 6 to 10 nm is formed on a p-type or n-type Si substrate 1,followed by forming a silicon nitride film 13 having a thickness of 100to 150 nm by using an LPCVD method and subsequently forming a siliconoxide film 14 having a thickness of 100 to 150 nm on the silicon nitridefilm 13.

[0060] In the next step, a trench 15 of STI is formed by using andoptical lithography and a RIE etching, followed by forming a surfaceoxide film having a thickness of 13 to 15 nm under an atmosphere ofoxygen and nitrogen at 1,000° C. By this surface oxidation, the edgeportion of the STI structure is rendered roundish so as to produce theeffect of moderating the electric field concentration in the edgeportion during operation of the semiconductor device.

[0061] In the next step, a first device isolation insulating film 16made of, for example, SiO₂ or O₃-TEOS is formed by the LPCVD or PECVD(Plasma Enhanced Chemical Vapor Deposition) in a manner to cover thetrench 15, as shown in FIG. 5B. In this case, if the opening width ofthe trench 15 is decreased because of the miniaturization of thesemiconductor device so as to increase the aspect ratio, which is aratio of the depth to the opening width of the trench 15, the surfacesof the first device isolation insulating film 16 grown from the innerwall of the trench 15 are brought into mutual contact in the center ofthe separation width. It follows that the first device isolationinsulating film is deposited in a manner to be seemingly folded insidethe trench 15.

[0062] Further, the surface is planarized by the chemical mechanicalpolishing (CMP) method and, then, the silicon oxide film 14 is removedby a wet etching method as shown in FIG. 5C. It should be noted that thecontacted portion of the surfaces generated in the first deviceisolation insulating film 16 in the step shown in FIG. 5B cannot beremoved by the planarizing and removing steps so as to remain as a seam17 in the central portion of the first device isolation insulating film16 buried in the trench 15, as shown in FIG. 5C. The seam 17 is renderedprominent particularly when the separation width of the STI is small.

[0063] As described previously, the seam 17 forms the nucleus of growthof the Si or SiGe particles in the selective epitaxial growing step ofthe Si or SiGe layer 10 so as to cause the selectivity degradation.Therefore, the following treatment is applied so as to prevent the seam17 from appearing on the surface of the device isolation insulatingfilm.

[0064] Specifically, the surface of the first device isolationinsulating film 16 made of, for example, SiO₂ or O₃-TEOS, which is onceburied in the trench 15, is etched with a diluted hydrofluoric acid soas to decrease the thickness of the first device isolation insulatingfilm 16 by about 100 nm. It is also possible to employ a RIE method forthe etching of the surface of the first device isolation insulating film16. Then, the groove formed in the open portion of the trench 15 by theetching (reduction in the thickness) of the surface region of the firstdevice isolation insulating film 16 is covered with a second deviceisolation insulating film 18 made of SiO₂ or O₃-TEOS, as shown in FIG.5D. In this case, the aspect ratio of the groove is smaller than theaspect ratio of the trench 15 shown in FIG. 5A so as to achieve a goodburied state of the second device isolation insulating film 18 in thegroove, though the separation width of the STI is small.

[0065] As described above, if the depth of the groove formed in the openportion is made smaller than the minimum diameter (separation width ofthe STI) of the open portion of the trench by allowing the surface ofthe first device isolation insulating film 16 to retreat from the opensurface of the trench, the second device isolation insulating film 18can be buried in the groove in a good buried state. It follows that itis possible to prevent the second device isolation insulating film 18buried in the groove from including a seam in the central portionrelative to the kinds and qualities of many insulating films and thegrowing conditions.

[0066] In the next step, a CMP treatment is applied with the siliconnitride film 13 used as a stopper so as to planarize the surface of thesecond device isolation insulating film 18, with the result that theseam 17 does not appear on the surface, as shown in FIG. 5E. Finally,the silicon nitride film 13 is removed by etching so as to form the STIstructure in which the seam 17 is not present on the surface, as shownin FIG. 5F. Then, if a semiconductor device comprising the CMOS circuitis formed by the manufacturing process described previously inconjunction with the first embodiment, it is possible to avoid thedefective device isolation characteristics caused by the selectivitydegradation in the selective epitaxial growth process of the Si or SiGelayer required for the formation of the elevated source/drain structure.

[0067] The present invention is not limited to the embodiments describedabove. For example, it is possible to allow the first device isolationinsulating film to retreat until the seam generated inside the firstdevice isolation insulating film does not remain in the first deviceisolation insulating film in the second embodiment of the presentinvention. In this case, the STI structure is equal to that shown inFIG. 4, except that the seam inside the first device isolationinsulating film is removed. However, if the aspect ratio of the grooveis decreased to such an extent that the seam does not appear on thesurface of the second device isolation insulating film in burying thesecond device isolation insulating film in the trench above the firstdevice isolation insulating film, no particular problem is generated inthe device isolation characteristics of the resultant STI structure.

[0068] As described above, according to the semiconductor device of thepresent invention, it is possible to ensure the contact area on thesource/drain region regardless of the miniaturization of the transistorstructure caused by the scaling, with the result that the connection tothe wiring via the contact hole is facilitated so as to decrease theseries resistance of the MOS transistor. Also, it is possible to ensurea high surface selectivity between the surface of the device isolationinsulating film and the substrate surface on the source/drain diffusionlayer regardless of the miniaturization of the STI structure so as tomake it possible to provide a semiconductor device formed of ahigh-performance MOS transistor having satisfactory device isolationcharacteristics.

[0069] Additional advantages and modifications will readily occur tothose skilled in the art. Therefore, the present invention in itsbroader aspects is not limited to the specific details andrepresentative embodiments shown and described herein. Accordingly,various modifications may be made without departing from the spirit orscope of the general inventive concept as defined by the appended claimsand their equivalents.

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 13. A method ofmanufacturing a semiconductor device, comprising: forming a gateelectrode on a semiconductor substrate with a gate insulating filminterposed therebetween; forming shallow source/drain diffusion layer inthose regions of said semiconductor substrate which are positioned onboth sides of said gate electrode by means of ion implantation performedwith said gate electrode used as a mask; forming a first side-wallinsulating film on said semiconductor substrate after formation of saidshallow source/drain diffusion layers; forming a second side-wallinsulating film on said first side-wall insulating film; etching back alaminate structure including said first side-wall insulating film andsaid second side-wall insulating film; removing said second side-wallinsulating film remaining on the side-wall portion of said gateelectrode so as to form an L-shaped/reversed L-shaped side-wallstructure consisting of said first side-wall insulating film coveringsaid gate electrode side-wall portion and a part of the upper surface ofsaid semiconductor substrate in the vicinity of said gate electrode;forming a semiconductor layer thicker than said first side-wallinsulating film on said semiconductor substrate by means of a selectiveepitaxial growth method so as to form an extending portion of saidsemiconductor layer on said first side-wall insulating film covering apart of the upper surface of said semiconductor substrate; and formingdeep source/drain diffusion layers in those portions of saidsemiconductor substrate which are positioned on both sides of said gateelectrode by means of ion implantation performed with said gateelectrode equipped with the side-wall structure used as a mask.
 14. Amethod of manufacturing a semiconductor device according to claim 13,further comprising forming a buried device isolation region consistingof a trench having an insulating film buried therein and positionedcontiguous to the outer peripheral portion of said deep source/draindiffusion layers, wherein the process of forming said buried deviceisolation region comprises: forming a trench in a semiconductorsubstrate; burying a first insulating film having a seam in a centralportion of said trench width along the inner wall of said trench;removing said first insulating film deposited outside said trench so asto planarize the surface of said semiconductor substrate; etching saidfirst insulating film so as to allow the surface of said insulating filmto further retreat; burying a second insulating film in a manner tocover said first insulating film remaining in the bottom portion of saidtrench; and removing that portion of said second insulating film whichis deposited outside said trench.